1. Technical Field:
The present invention relates to a lining material for lining pipe lines, especially gas conduits, city water pipe lines and pipe lines for construction of power transmission wires or telecommunication cables, chiefly those buried in the ground, for the purpose of repair or reinforcement of the pipe lines.
2. Background Art:
In recent years, a method of applying a lining material onto the inner surface of city water pipe lines, gas conduits and construction pipe lines for power transmission wires or telecommunication cables is carried out for the purpose of repair or reinforcement of the pipe lines when superannuated. The method of applying a lining material is carried out in such manner that a flexible lining material in the form of a tube previously provided on the inner surface thereof with a binder is inserted into a pipe line and allowed to advance therein while turning the lining material inside out and pressing it against the inner surface of the pipe line under fluid pressure whereby the inner surface of the lining material is bonded onto the inner surface of the pipe line by the aid of the binder. According to this method, it is unnecessary to dig up a pipe line over its full length. The method has such merits that the lining work can be done within a short period of time for a long pipe line and is operable for a pipe line having a number of bends, thus being watched especially in recent years as a very excellent method.
As a lining material utilizable for this method should be flexible and air-impervious and is required to possess satisfactory strength in lengthwise and diametrical directions of the pipe line in consideration of any influence of creeping or earthquake occurring after lining, a tubular textile jacket having a film of a synthetic resin on the exterior surface thereof has hitherto been used as the lining material.
The filmy layer of the lining material is required to possess various characteristics such as flexibility, stretchability of a moderate degree and strength as well as good heat-resistance, abrasion-resistance and scratch-resistance.
In case of a lining material to be applied to city water pipe lines, a synthetic resin constituting the filmy layer should particularly be safe to the quality of water. A material utilizable for city water pipe lines is required to satisfy the specifications defined in individual countries, for example, those defined by the Japan Water Works Association (JWWA) in case of Japan. According to the specifications defined by JWWA, the material is required to satisfy the test for quality of water defined by ("Tar Epoxy Resin Paints for Water Works and Method of Coating " (K-115) wherein the specifications are defined in detail for turbidity, color scale, the amount of consumption of potassium permanganate, the amount of consumption of chlorine, etc. A synthetic resin of polyolefin series as well as a synthetic resin of fluorine series is specified as a resinous material forming the filmy layer of a lining material satisfying these specifications.
Of these synthetic resins, the fluorine resin is very expensive and inferior in extrusion characteristics so that it is not suited as a resinous material forming the filmy layer of a lining material for the pipe lines. Accordingly, the resinous materials for this application are substantially restricted to a synthetic resin of polyolefin series.
The synthetic resin of polyolefin series includes high density polyethylene-resin, medium density polyethylene resin, low density polyethylene resin, polypropylene resin, polybutene resin, etc. However, the resins other than low density polyethylene are inferior in flexibility, while the low density polyethylene is inferior in durability. Thus, these resins were not necessarily suitable as a material constituting the filmy layer of a lining material for pipe lines.
3. Prior Art:
The present inventors already devised as a lining material for city water pipe lines a material using a linear low density polyethylene resin or a material using a blend of polyethylene resin and pure styrene-ethylene butylene-styrene resin free from polypropylene resin and an oily substance for the filmy layer (Japanese Utility Model Applns. Nos. Sho. 58-176565 and 59-44499).
The linear low density polyethylene resin used in the lining material of the above mentioned Japanese Utility Model Appln. No. Sho. 58-176565 is a synthetic resin of polyolefin series comprised predominantly of ethylene, which is obtained by copolymerizing ethylene with an .alpha.-olefin. The resin having a density of about 0.910-0.940 g/cm.sup.3 belongs to a low density polyethylene resin and has a molecular structure similar to a linear high density polyethylene resin almost devoid of branched chains. This linear low density polyethylene resin is of such characteristics that the tensile strength is as high as about 330 kg/cm.sup.2 and equals to that of a high density polyethylene resin and that the stress-crack resisting property is longer than 1000 hours to show excellent durability while possessing softness as seen in a low density polyethylene resin.
In general, polyethylene has good chemicals-resisting property. In case polyethylene is put in the state of receiving stress or retains stress at the time of being processed, however, polyethylene may form cracks when brought into contact with a certain kind of liquid or vapor. This phenomenon is called stress-crack. The stress-crack resisting property referred to herein is measured according to a testing method specified in ASTM-D-1693 wherein a polyethylene resin is allowed in the state of receiving a definite amount of stress to stand in a given environment and the resisting property is given in terms of a period of time elapsing until cracks are formed. This property is one of the standards for durability of polyethylene resins and is very important as a characteristic property required for pipe lines for passing water therethrough, especially in the event the lining material is smaller in diameter than the pipe lines and is pressed against them by expansion of the diameter of the lining material for lining.
The styrene-ethylene butylene-styrene resin used for the lining material of the above mentioned Japanese Utility Model Appln. No. Sho. 59-44499 is generally called an elastomer of styrene series and is a resin which is most excellent in rubbery elasticity among the thermoplastic elastomers substituted for vulcanized rubber. This styrene-ethylene butylene-styrene resin is characterized in that the residual double bond has been hydrogenated which exists in the central rubber block of a styrene-isoprene-ethylene block copolymer and that insufficient stability of the copolymer against heat and weathering action has remarkably been improved. The styrene-ethylene butylene-styrene resin is stable against heat and extremely flexible so that the resin has properties most desirable as a material for the film in the lining method.
However, it is rare that this styrene-ethylene butylene-styrene resin is used singly. In general, a commercially available "styrene-ethylene butylene-styrene resin" is inferior in stress-crack resisting property and fluidity so that the resin is incorporated with polypropylene having good compatibility therewith to improve stress-crack resisting property and with an oily substance to improve water-flowability and flexibility. As a result of tests on the quality of water, however, it has been found that a stabilizer in the polypropylene and the oily substance in the above mentioned commercially available "styrene-ethylene butylene-styrene resin" ooze out on the surface of the resin to increase the amount of consumption of chlorine in an undesirable manner. This commercially available "styrene-ethylene butylene-styrene resin" will be referred to hereinafter as the styrene-ethylene butylene-styrene resin composition.